add func_detail_nonsolid

[RealGamerX]

Currently, if you want to add a non-solid brush to your map, your only option is to use a brush entity, such as func_illusionary or func_brush. Brush entities take up valuable edicts, and are generally overkill when all you want is a brush you don't collide with.

This PR adds func_detail_nonsolid, which, just like func_detail, gets turned into a world brush on compile, thus not consuming any edicts. It basically acts like the %compilenonsolid VMT property.

Just like func_detail, func_detail_nonsolid has no keyvalues.

Here's the entity in action:

func_detail_nosolid.mp4

Huge thanks to @gidi30 and @flurbury for helping me with stopping windows from breaking the entity.

[chanticleerhegemony]

func_detail_illusionary would be a better name to ensure consistency with other quake derivatives

[SirYodaJedi]

func_detail_illusionary would be a better name to ensure consistency with other quake derivatives

As well as consistent with func_illusionary.